1. Field of the Invention
This invention relates to turbocharger control and more particularly relates to preventing overspeed of a turbocharger.
2. Description of the Related Art
Turbochargers have been a common feature on combustion engines to enhance performance. Continuing demand for power density and torque combined with emissions regulations have required continuous innovation in turbocharger hardware and control systems. Hardware related to turbocharger control like wastegates, bypass valves, variable geometry, and adjustable vanes have been known in the art for some time. While improvements in turbocharger hardware are ongoing, turbocharger control systems are largely challenged by limits imposed by present computer processor speeds and turbocharger speed sensor detection speeds, which contribute to a lack of control precision during transient events in real time applications.
Present turbocharger control systems are primarily reactive systems that track only one or two system parameters to determine turbocharger speeds. Reactive turbocharger control systems using limited system parameter input may fail to predict turbo speed transient events. Therefore, present turbocharger control systems must choose between aggressively responding turbocharger control that experiences overshoot of target speeds in highly transient events, or less responsive turbocharger control that may not experience overshoot, but that experiences reduced transient performance. A turbocharger experiencing overspeed can fail immediately, or experience excessive wear on turbocharger parts resulting in reduced service life and reliability.
Some present turbocharger systems include more than one turbocharger stage. These systems allow greater charge densities and compression of intake air. Further, they allow the inclusion of a smaller, high pressure turbocharger to improve turbocharger response, and the inclusion of a larger, low pressure turbocharger to improve turbocharger flow capacity. However, small turbochargers are even more susceptible to overspeed conditions in transient events due to the low mass of the turbine wheel.